Photochromic schiff base copolymers



United States Patent PHOTOCHROMIC SCHIFF BASE COPOLYMERS Joseph E.Kovacic, St. Paul, Minn., assignor to Sperry Rand Corporation, New York,N.Y., a corporation of Delaware No Drawing. Filed Apr. 25, 1967, Ser.No. 633,423 Int. Cl. C082 33/02, 29/46; C09k 1/00 US. Cl. 260-47 10Claims ABSTRACT OF THE DISCLOSURE Photochromic Schiff base copolymersare prepared by copolymerizing a photochromic Schiff base which issubstituted with an unsaturated hydrocarbon group with an unsaturatedmonomer, such as styrene and methyl methacrylate. The resultingphotochromic copolymer material can then be converted to thin filmmaterial for use in displays and/or memory systems. Examples ofphotochromic Schilf bases substituted with an unsaturated hydrocarbongroup which are useful in the preparation of the above-identifiedphotochromic copolymer materials include 3-allylsalicylidene aniline,3-allylsalicylidene-2',4-dirnethyl-aniline,3-allylsalicylidene-o-chloroaniline, 3-allylsalicylidene-o-iodoaniline,3-allylsalicylidene-2',4'-dichloroaniline,3-allylsalicylidene-2',4-dibromoaniline,3-allylsalicylidene-3',4',5-trichloroaniline and 3-allylsalicylidene-2',4',6-trichloroaniline.

BACKGROUND OF THE INVENTION Many of the Schifi bases, the reactionproduct of an aldehyde with a primary amine, prepared by reactingsalicylaldehyde and substituted salicylaldehydes with anilines are knownto be photochromic. Photochromism is the term employed to describe thephenomenon of a change in the color of a material which occurs onexposure to ultraviolet (U.V.) radiation, followed by return to theoriginal color on exposure to radiation, usually visible, of a differentwave length or on storage in the dark. Most of the known salicylideneanilines are colored some shade of yellow in the ground state but whenexposed to ultraviolet radiation the photochromic salicylidene anilinesbecome colored orange to red. In the dark this color is retained forvarying periods of time. However, the colored or excited state can bereturned to the ground state color very quickly by exposure to intensevisible radiation.

In computer memory systems or displays it would appear that photochromicmaterials would be more advantageously employed in the form of a filmrather than as crystalline aggregates. Various film forming materialsare known which contain dispersed or dissolved photochromic materials ina plastic which has very nearly the same refractive index as thephotochromic material itself. Compounds employed in such products, e.g.the spiropyrans, however, have the tendency to fatigue after a number ofexposures to ultraviolet radiation, followed by exposure to visibleradiation. Fatigue appears to be associated with an irreversiblereaction upon exposure to ultraviolet radiation energy.

Therefore, it is an object of this invention to produce ice a materialwhich is not only capable of being cast or produced or otherwisefabricated into film-form but which is also photochromic per se.

Another object of this invention is to convert a known photochromicmaterial, such as a photochromic salicylidene aniline, to a materialwhich is capable of being formed or fabricated into a film but whichalso in the film-form exhibit photochromic properties.

SUMMARY OF THE INVENTION It has been discovered that photochromic Schifibases when substituted with an unsaturated hydrocarbon group, such as inthe salicylidene portion of a Schiif base derived by reacting asalicylaldehyde with a primary amine, and then copolymerized with anunsaturated monomer, such as styrene and methyl methacrylate, producephotochromic copolymer materials which can be converted to thin filmmaterials suitable for use in computer display and/or memory systems.Specifically, and in accordance with one embodiment of this invention,it has been discovered that a copolymer of methyl methacrylate and 3allylsalicylidene 3,4',5' trichloroaniline is not only photochromic atroom temperature but is also capable of being converted to a thin filmmaterial.

A Schiif base is the reaction product of an aldehyde with a primaryamine. Many of the Schifi bases prepared by reacting salicylaldehyde andsubstituted salicylaldehydes with aniline and substituted anilines areknown to be photochromic. If such Schilf bases are substituted with anunsaturated short chain hydrocarbon group on one of the rings theresulting material could then readily be copolymerized with unsaturatedmonomers, e.g., vinyl monomers, such as methyl methacrylate and styrene.The resulting copolymer would retain the photochromic structure of theunsaturated hydrocarbon substituted Schiif base intact. For example, acommercially available material 3-allysalicylaldehyde having thestructural formula could be reacted with a substituted aniline, such asa substituted aniline having the formula n NH -X wherein X is H, F, Cl,Br, I CH or combinations thereof, to yield a Schiff base. In theinstance where the substituted aniline is 2,4,6-trichloroaniline, therewould be produced the Schiff base3-allysalicylidene-2',4,6-trichloroaniline having the structuralformula:

OH =N C1 The resulting unsaturated hydrocarbon substituted Schilf base,3-allylsalicylidene 2,4',6'-trichloroaniline although extremelydiflicult to polymerize alone can be readliy polymerized with a vinylmon mer, such as methyl methacrylate or styrene to yield, in the case ofstyrene, the photochromic copolymer having the structural formula (IV)om-on om-on am-on -CH=N Cl wherein Y is an integer greater than one,usually in the range 5-100, more or less. As appears from the structuralformula of the above illustrative photochromic copolymer prepared inaccordance with this invention, the basic, photochromic structure of thesalicylidene aniline component remains intact and, accordingly, retainsits photochromic properties and imparts its'phot chromic properties tothe resulting copolymer.

The allylsalicylidene anilines employed in accordance with the practiceof this invention for reaction or copolymerization with an unsaturatedmonomer, such as styrene and methyl methacrylate, were prepared byreacting 3-allylsalicylaldehyde with aniline or a substituted anilineeither in the presence of absence of a solvent. The following examplesare illustrative of the preparation of allylsalicylidene anilines:

Example 1 3-allylsalicylidene aniline.Equimolar amounts of 3-allylsalicylaldehyde and aniline in methanol were heated at reflux for30 minutes and allowed to cool. A small sample was evaporated to removemethanol and the liquid residue tested tested by means of an infraredspectrophotometer. The infra-red spectrum indicated that reaction wascomplete. The methanol was evaporated from the remaining reactionmixture and an orange-yellow oil remained which could not becrystallized. The product was not photochromic at room temperature butwas fluorescent at liquid nitrogen temperature. When copolymerized withstyrene or methyl methacrylate, a copolymer resulted which wasfluorescent and photochromic at the temperature of liquid nitrogen.

Example 2 Approximately 2% solutions of (V) in styrene and methylmethacrylate were copolymerized thermally. In addition, a '2-componentpotting material which is a catalyzed acrylate system was used as thematrix for copolymerization tests. The resulting copolymers werephotochromic and fluorescent at the temperature of liquid nitrogen.

Example 3 3-allylsalicylidene-o-chloroaniline.A solution of 1.622 g.(0.01 mol) of o-chloroaniline was heated at 60 C. for three hours in 10ml. of ethanol. At the end of this time, an infra-red scan indicatedthat very little reaction had occurred. Therefore, the ethyl alcohol wasevaporated and the residue heated at -125 C. for one hour. An infra-redscan then indicated that the reaction was completed. The product was ayellow oil. When the product was copolymerized with styrene and withmethyl methacrylate the resulting copolymers were found to bephotochromic and fluorescent at the temperature of liquid nitrogen.

Example 4 3-allylsalicylidene-o-iodoaniline.-A solution of 1.622 g.(0.01 mol) of 3-allylsalicylaldehyde and 2.19 g. (0.01 mol) ofo-iodoaniline in 15 mol. of ethanol was heated to reflux for 30 minutes.No color change occurred indicating that no reaction had taken place.The ethanol was evaporated and the residue heated for 30 minutes at C.at which time the infra-red spectrum showed that the reaction wascompleted. The product was a reddish-orange oil which could not becrystallized. When the product was copolymerized with styrene and .withmethyl methacrylate the resulting copolymers were found to bephotochromic and fluorescent at the temperature of liquid nitrogen.

Example 5 3-allylsa1icylidene-2',4dichloroaniline.-A mixture of 1.622 g.(0.01 mol) of 3-allylsalicylaldehyde and 1.62 g. (0.01 mol) of2,4-dichloroaniline was heated on a hot plate in a beaker until aninfra-red spectrum showed that the reaction was completed. The productwas recrystallized from petroleum ether (3070 C.) to obtain brightyellow needles. This Schiif base is photochromic under UV. excitation.When the product was copolymerized with styrene and with methylmethacrylate the resulting copolymers were found to be photochromic andfluorescent at the temperature of liquid nitrogen.

Example 6 3-allylsalicylidene 3',4',5 trichloroaniline.Equimolar amountsof 3-allylsalicylaldehyde and 3,4,5-trichloroaniline were heated andreacted until an IR scan indicated that the reaction was completed. Oncooling, the product formed a crystalline mass which was recrystalllzedtwice from isopropanol to give orange-yellow large needles of theproduct. When the product was copolymerlzed with styrene and with methylmethacrylate the resulting copolymers were found to be photochromic atroom temperature.

Example 8 3 allylsalicylidene 2, 4', 6' trichloroaniline.3.244 g. (0.02mol) 3-allylsalicylaldehyde, 3.93 (0.02 mol) of 2,4,5-trichloroanilineand 40 ml. of n-amyl alcohol were heated to reflux (ca. C.) for a totalof 72 hours. A sample was removed, evaporated and the residue testedabout every 12 hours during the heating period in order to determinewhen the reaction was completed. At the end of 72 hours, the reactionwas not yet completed, but heat was discontinued and the n-amylevaporated. Twenty 3,483,162 6 ml. of petroleum ether (30-70 C.) wereadded to the carbon atoms, vinyl esters, such as vinyl acetate and oilyresidue and the solution placed in a freezer overvinyl propionate, thevinyl and vinylidene chlorides, stynight. An infra-red spectrum of theprecipitated crystalline rene-butadiene mixtures,styrene-butadiene-acrylonitrile showed it to be contaminated withstarting material. It mixtures, ethylene, propylene andethylene-propylene was therefore recrystallized two additional times andthe systems, acrylonitrile, acrylamide, N-vinyl pyrrolidone,contaminants were thereby removed. The compound was 5 methyl vinylketone, methyl isopropenyl ketone ethyl found to be photochromlc tinderradlauon' f vinyl sulfone, butyl vinyl sulfone, methacrylonitrile, theProduct was copolymenzed Wlth Styrene and wlth vinylene carbonate,a-methylstyrene, vinyl toluene, N-

methyl methacrylate the resultmg copolymers were found vinyl car-bazole,vinyl ethers 4-phenylbutene-l, acrylonigu pholochromlc at thetemPm'ature of hqmd mtro' 10 trile-isopropenyl toluene systems, vinylchloride-vinyl acetate systems, vinyl chloride-vinylidene chloridesystems and mixtures of the foregoing.

Substituted allylsalicylidene anilines were copolymercopolymenzatlon ofthefubstltuted schlff ized with styrene and with methyl methacrylate byheatlvlth t unsaturated {monomer accordance Wlth f ing in the absence ofa catalyst. Additionally, a -2-commventlon may be calmed out any of thecatalytlc ponent methacrylate potting compound was used as a potornon-catalytic polymerization techniques. The unsatuting matrix. All thecopolymers were found to be=photorated g p y be located at substantiallyy p chromic at liquid nitrogen temperatures. In addition, tion in thesubstituted Schiif base, either in the salicylalany of the copolymerswere found to be fluorescent. The dohyde portion or in the anilene ringportion of the complete results of these tests are set forth in accom-Schifi base, the only requirement being that the substi- Example 9panying Table I: tuted Schifi base be capable of polymerization,thermally TABLE I Physical UV exposure of Compound state pure compoundUV exposure of copolymers l 3-allylsallcylidene aniline Liquid..- N oinfect- Fluorescent and photochromic at liquid N2 temperature.3-al1ylsalicylidene-o-chloroanlline. do do Do.3-allylsalicylidene-o-lodoaniline d .do Do.3-a'llylsalicylidene-2,4dimethylanihne Photochromic D0.3-allylsalicylidene-3'4,5'-triehloroaniline do do Photochromic at roomtemperature. 3-allylsalicylidene-3,4,6-trichlor0ani1iue do doPliotochromic at liquid NI temperaure.

In methyl methacrylate, in a mixture of styrene and methyl methacrylate,and in a 2-component potting compound (a catalyzed acrylate system).

Example 10 or catalytically, by addition with the unsaturated mono-3-allylsalicylidene-3,4,5-trichloroaniline was cot th 1 ti of th ubstipolymerized wltll methyl mtlthacrylate a temperzllture tute li gh ii fba s t Wit h ili i l r i sait fii at miono inir the f gggizfgg g g g sfiggi xg iigfif g if reaction ratios are usually in the range such thatthe a to be photochrom'ic at room temperature and to Schilf basecomprises less than about 10% of the reacbe strongly photochromic andfluorescent at liquid nitro- 22 l g 'gg gzgig i gz g g irzg g g ii gg fgen temperature 1 57 by weight since it appears that when the Schiif ggi j gi i gz i gg g g g g gg base comprises more than 10% of thereactants the Schifi bases employed in the practices of this inven- 3 Tof the resultmg copolymer are adversely aftion for the polymerizationwith an unsaturated monomer are characterized by containing in thehydrocarbon group The copolymer produced in accordance with this mvention can be converted into film-form by hot pressing or chain anunsaturated linkage, such as the ethylene group CH:cH2) or the allylgroup by dissolution 1n a solvent followed by evaporation of the solventor by carrying out the copolymerization of 2 2) the reactants betweensuitable substrate surfaces, such Although the allyl group as thsubstituent unsatas glass plates, to produce directly a thin iilml ofthe urated short hydrocarbon has been found particularly copolymer- Thepotfmg compound e p d f tests satisfactory as the unsaturatedsubstituent hydrocarbon demonstratlve and lllustranve 'P mventlon 1Sslmply group, other unsaturated, relatively short chains, e.g. conaz'component mlxture conlammg a catalyst and P taming from 2 to 7 carbonatoms Per group, are uSefuL dered acrylate or methacrylate ester as onecomponent and The unsaturated monomers particularly useful in amonomeric acrylate or methacrylate ester as the other cordance with thisinvention for copolymerization with f f- When these matenals are mlxedthe result the Schiif bases in accordance with this invention include Ematenal r P a f f P l and styrene and the various acrylates,particularly the methaclls P 1 9 111 the p l 0f thls 11'l VeI1 t10I1 15to Serve rylates, such as the alkyl acrylates and the alkyl methas asultalile OI I1Ve111611t P0 Y y acrylates, e.g., methyl methacrylate,ethyl methacrylate, As will be apparent to those skilled in the art inpropyl methacrylate, butyl methacrylate and the like. the light of theforegoing disclosure, many substitutions, Other unsaturated monomerswhich are useful in the alterations and modifications may be made in thepracpreparation of photochromic copolymers in accordance tice of thisinvention without departing from the spirit with this invention includethe acrylate and methacrylate or scope h f, esters having the structures1 l i 1. A photochromic addition copolymer derived by reacting anunsaturated monomer and a salicylidene aniline containing a substituentunsaturated hydrocarbon group, the salicylidene aniline comprising lessthan about wherein R is an alkyl, aryl or aralkyl group, the alkyl 10%by weight of the reactants employed in producing group or moietypreferably containing not more than 6 said photochromic copolymer.

2. A copolymer in accordance with claim 1 wherein said unsaturatedmonomer is selected from the group consisting of styrene and anacrylate.

3. A copolymer in accordance with claim 1 wherein said salicylideneaniline is 3-allylsalicylidene aniline.

4. A copolymer in accordance with claim 1 wherein said salicylideneaniline is 3-allylsalicylidene-2',4-dimethylaniline.

5. A copolymer in accordance with claim 1 wherein said salicylideneaniline is 3-allysalioylidene-0-chloroaniline.

6. A copolymer in accordance with claim 1 wherein said salicylideneaniline is 3-allylsalicylidene-o-iodoaniline.

7. A copolymer in accordance with claim 1 wherein said salicylideneaniline is 3-allylsalicylidene-2,4'-dichloroaniline.

8. A copolymer in accordance with claim 1 wherein said salicylideneaniline is 3-allylsalicylidene-2',4'-dibrornoaniline.

9. A copolymer in accordance with claim 1 wherein UNITED STATES PATENTS3,141,903 7/1964 Fertig et 3.1. 3,186,968 6/1965 Fertig et a1. 3,190,8606/1965 Fertig et al.

3,290,270 12/1966 Goldberg et al.

HARRY WONG, JR., Primary Examiner US. Cl. X.R.

@ 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO.Dated 9,

Inventor(s) JOSEPH E. KOVACIC It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

In column 3, line 29, the word "of" (first occurrence) should correctlyread or line 39, the second "tested" should be removed. I

In column line 3, the phrase B-allylsalioylaldehyde and 1.27 g."(0.0lmol) of should be inserted after of"; 1ast line, "heat" should readheating -5 last line, after 'n--am5r] the word alcohol should beinserted.

In column 5, line 3, after "crystalline" the word product should beinserted; line 19, "any" should read many unde: Table I, the lastcompound listed should correctly read 3-al] salicylidene-2',H,6'-trichloroaniline SIGNED A'ND SEALED JUL 141970 @EAL) Anew v EdwardM. meta", 1;, 211mm 1:. sum, Arrestin 0m missimmor Patents

